1. Field of the Invention
The present invention relates to a high-frequency oscillation (HFO) patient ventilator system, in particular to an HFO system capable of providing assisted ventilation support for a spontaneous breathing effort and also to a monitoring device capable of detecting a spontaneous breathing effort during HFO ventilation.
2. Description of the Prior Art
An HFO ventilator supplies breathing gas to the airways of a patient via a patient circuit at a frequency of approximately 150 breaths per minute or more and with tidal volumes significantly less than required during spontaneous breathing, typically at or below anatomical dead-space volumes. This is in marked contrast to a conventional mechanical ventilator which typically supplies breathing gas to the patient circuit at a frequency and with a tidal volume close to the values during spontaneous breathing.
HFO ventilators are well known and generally have an oscillator which is connectable in gas communication with one end of the gas tubing of a patient circuit. The circuit terminates in an opposite end, such as in an endotracheal tube, for connection to a patient""s airways. The oscillator is then driven to vibrate a column of gas within the circuit to actively supply gas to and extract gas from the patient""s airway. An HFO ventilator also has a gas supply for providing a constant, continuous so called xe2x80x98biasxe2x80x99 flow to the patient. This bias flow intersects the oscillatory pathway and serves to maintain (bias) an average positive airway pressure about which the high-frequency oscillations generated by the HFO ventilator occurs, as well as to wash exhaled gasses from the circuit. Gas leaves the circuit through an expiratory limb, which is designed as a low pass filter. The bias supply of such systems is usually insufficient to supply sufficient gas to a patient if the patient should attempt a spontaneous breath.
One known patient ventilator system, which reduces this problem is disclosed in U.S. Pat. No. 5,165,398. The system has an HFO ventilator and a conventional mechanical ventilator connected to a patient breathing circuit, and cooperable to provide, in one mode of operation, a conventional low frequency, large tidal, volume time cycled mechanical ventilator supply having superimposed thereon high-frequency oscillations from the HFO ventilator. In another mode of operation this system can act as an HFO ventilator with the conventional mechanical ventilator providing the continuous bias flow at a level to maintain a constant pressure. A mechanical pressure regulator is provided in the patient circuit proximal the patient end which operates to increase this continuous bias flow and maintain the pressure as a patient attempts to breath spontaneously. A non-assisted spontaneous breathing support mode of operation is thereby provided.
It is an object of the present invention to provide a breathing-assist system which is operable to provide high-frequency oscillation ventilation to a patient, but which is also able to provide sufficient breathing support to the patient if the patient should attempt a spontaneous breath.
This object is achieved in a first embodiment of the invention having a patient ventilator system capable providing assisted support of a spontaneous breathing effort detected during high-frequency oscillation ventilation. Thus, by monitoring for changes in one or both of the gas pressure and gas flow during the operation of an HFO ventilator which are unrelated to the high-frequency oscillations produced by that ventilator, a spontaneous breathing effort can be detected and a gas supply, preferably a conventional mechanical ventilator, can be operated to supply breathing gas at a level to assist the detected spontaneous breathing effort.
This object also is achieved in a second embodiment of the invention wherein a detection device is adapted to monitor for changes in one or both of the gas pressure and gas flow during the operation of an HFO ventilator which are unrelated to the high-frequency oscillations produced by that ventilator and to provide an output signal dependent on the monitored changes to indicate one or more of a spontaneous breathing effort, a leak and hyperinflation.